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As the main objective of the research was to enhance the adhesion between steel and zinc, a considerable part of the activity has been devoted to the study of a method for evaluating such adhesion. A first tentative test was based on an artificial ageing treatment performed by backing the samples in a forced air oven, at 180 C for 5 minutes. The tested samples having 2 to 15 mg/m(2), and, in particular, the ones having over 5 mg/m(2) of surface carbon, showed that the number of blisters on the zinc surface increases with increasing surface carbon on the steel. This method is not able to distinguish little differences in the cleanliness of the steel surface, namely for a content of surface carbon that is below 5 mg/m(2).

For this reason, a further activity started with the aim to set up the hydrogen back charge technique. This technique consists of applying a cathodic current on the bare side of a one-side electrogalvanized steel sheet in an acid solution in order to cause the reduction of the hydrogen ion. It has been assumed that the resulting atomic hydrogen passes through the steel structure forming molecular hydrogen at the zinc-iron interface. The quantity of molecular hydrogen increases as the surface cleanliness and the surface homogeneity of the steel decreases. The formation of molecular hydrogen causes detachment of the zinc coating. .

Additional information

Authors: FERRARI V, Centro Sviluppo Materiali, Roma (IT);CAMPIONI M, Centro Sviluppo Materiali, Roma (IT);PACELLI L, Centro Sviluppo Materiali, Roma (IT)
Bibliographic Reference: EUR 17901 IT (1998) 52pp., ECU 10
Availability: Available from the (2)
ISBN: ISBN 92-828-3231-7
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